Cycling and heat exhaustion

[briansnail]

We did a long session on our bikes. Some of us felt dizzy and nauseous later.
Normally we are as fit as fiddles. A quick google reveals who have to drink lots of water in the heat. If your older you might not realise your dehydrated. Urine should be light coloured but people are cutting back on food as it hits 26 Centigrade. The healthy foods are low in salt anyway. So lt be light in colour but one still needs to drink more water.
How's you doing cycling in the heat?
**************************************
I ride Brompton and a 100% British Vintage

[ANTONISH]

We did a long session on our bikes. Some of us felt dizzy and nauseous later.
Normally we are as fit as fiddles. A quick google reveals who have to drink lots of water in the heat. If your older you might not realise your dehydrated. Urine should be light coloured but people are cutting back on food as it hits 26 Centigrade. The healthy foods are low in salt anyway. So lt be light in colour but one still needs to drink more water.
How's you doing cycling in the heat?
**************************************
I ride Brompton and a 100% British Vintage

One of the problems with hydrating is consuming large quantities of water can reduce sodium levels - so reducing salt intake can be counter productive.
My "recovery" method after a long ride is a bottle of soda water and a packet of lightly salted crisps.

[Jdsk]

We did a long session on our bikes. Some of us felt dizzy and nauseous later.
Normally we are as fit as fiddles. A quick google reveals who have to drink lots of water in the heat. If your older you might not realise your dehydrated. Urine should be light coloured but people are cutting back on food as it hits 26 Centigrade. The healthy foods are low in salt anyway. So lt be light in colour but one still needs to drink more water.
How's you doing cycling in the heat?
...

One of the problems with hydrating is consuming large quantities of water can reduce sodium levels - so reducing salt intake can be counter productive.
...

Overhydration is being increasingly recognised, and can cause severe neurological problems. That's "dilutional hyponatraemia" with the low plasma sodium concentration to which ANTONISH refers.

Here's the NHS advice:

"Heatwave: how to cope in hot weather":
https://www.nhs.uk/live-well/seasonal-h ... t-weather/

"Heat exhaustion and heatstroke":
https://www.nhs.uk/conditions/heat-exha ... eatstroke/

And note that it does not mention using the colour of urine as a warning sign of dehydration or as a target for adequate hydration. Colour of urine may not be reliable and that "should be" could be dangerous advice. Previous discussion of this:
viewtopic.php?p=1496077#p1496077
viewtopic.php?p=1519635#p1519635


Jonathan

[Cugel]

Two things to watch for when cycling in the heat:

If its also humid, you may find you can't sweat to lose body heat as easily as you normally do. You can become heat-exhausted when your body temperature goes up more than you realise, as the sweat remains unevaporated on your skin and in your clothes. It's the evaporation of your sweat that does a lot of the cooling.

If it's very dry as well as hot, you can sweat freely and not notice as the salty stuff evaporates so quickly. You're cooling but can become quickly dehydrated and maybe low on the blood salts. No sweat left? You'll heat up.

Another factor, not so much due to temperature but rather to the radiant heat from the sun, is that those sunny very clear air days mean more UV is falling on your personage, potentially crisping your skin. Factor 50 in copious amounts is advisable, especially on the upward facing bits like ear-tops and forearms. A cooling wind can disguise the fact that you're being slowly fried, until its too late and you are "lobster".

Cugel

[briansnail]

The sugar laden drinks where you add water to concentrate have to much sugar.Even if they are so nice with lots of clinky ice cubes.I find if i boil a kettle and mix water so it is tepid I can drink lots more.Of course some will be the opposite and find that they down more ice cold.
At work some people have a theory that hot tea or coffee actually cools you down more long term.Not sure if fact or fiction.

[Psamathe]

From a non-medical perspective I think different people tolerate heat and it's effects differently. From my various travels I seem to handle heat a lot better than many others i.e. on quite a few occasions others really suffering whilst I'm only beginning to show maybe initial signs.

Ian

[Nearholmer]

I’ve only managed to make the dehydration mistake once in recent years, on one of those days of warm sun, and pleasantly evaporating light breezes that Cugel mentions, where sweat is whipped away without even being noticed, and what surprised me was how it hit suddenly. One minute feeling fine, the next not great at all, and the last ten miles home a real endurance test.

The lesson in that for me was to drink before feeling thirsty, not great sloshing gallons, but periodic small top-ups.

Often, I don’t notice I’m thirsty until I stop for a drink / it’s as if the act of cycling overtakes the thirst feeling.

[simonineaston]

Half-way through an interesting biography of Paul Dirac, I checked this morning to see how far away the Sun is (it's 93,000,000 miles, give or take). I get that it's a big ball of burning hydrogen, but what's really interesting is that all the radiation (heat, light and all the unseen stuff that blasts our skin) gets here across 'the vacuum of space'!!
ps clever folks ie not me will know that it turns out it's not really a vacuum at all!!

[simonineaston]

my naive assumption had been that light being wave-like, it would need a medium in which to travel... that is to say, if you you throw a pebble into a pond you get ripples; if no pond, no ripples...

[Jdsk]

my naive assumption had been that light being wave-like, it would need a medium in which to travel... that is to say, if you you throw a pebble into a pond you get ripples; if no pond, no ripples...

There's two different problems with that...

Light isn't only wave-like, it's also particle-like:
https://en.wikipedia.org/wiki/Wave–particle_duality

And the assumption that a wave needs a medium. Apart from wave-particle duality it has been experimentally shown that the speed of light is the same in all directions. That's what ended the usefulness of the idea that light has a special medium: the luminiferous ether:
https://en.wikipedia.org/wiki/Luminiferous_aether

Jonathan

[axel_knutt]

Others used to think I was eccentric for carrying 4 litres of water on the bike, but on hot days I used to get through all of it, and sometimes stop to buy more. One day walking on the South West Way the sweat was dripping off the hem of my T shirt, and I didn't pee all day despite drinking all the 3-4 litres I was carrying. I have been known to stop and knock on stranger's doors asking for a top-up.

On a couple of occasions I've arrived at a hostel reception and found that I was unable to write my name and address, my brain just wouldn't make my fingers move where I wanted them to. One was a hot day, but I don't recall whether the other was.

[axel_knutt]

If its also humid, you may find you can't sweat to lose body heat as easily as you normally do.

A wet bulb temperature of 35C is the limit to human survival:

[foxyrider]

I must admit that it has happened to me on several occasions, not always when riding either. I can be a bgr when it comes to eating and drinking when riding, i literally forget to do either, i've finished rides in excess of 100km without touching the food or drink i have with me - and i always have at least a bottle of water on all my rides. although i can finish a ride rimed with salts its the humid heat that gets me in a pickle, i'll end up stopping often for shade, utilising any water feature to help cool off.

You can see in this shot from the 176km Eddy Merckx Classic in the mountains east of Salzburg in 2016, the rime on my jersey but what is not so obvious is a similar coating on my arms and legs. Temperatures on the day reached over 35c, at @ 120km i did need a shade stop and a good dose of wet! You can see i was carrying @ 1.5l of drink from the start, i refilled twice on the way round and took on supplementary drinks at each stop, the stein of beer at the end didn't touch the sides!

On one occasion in Germany i set off on a warm but misty morning which soon changed to very heavy and muggy as i climbed out of the valley, by the time i'd covered 15km i was done in. Luckily at the next village was a small fountain in the street which i used to cool down, only just stopping short of climbing in! By this time the skies had cleared and the cause of my 'exhaustion' had departed, after that i had no further issues.

As regards hydration/cooling effects, a cold beverage does give immediate gratification but i find hot tea has a longer lasting effect, i'll often have both when i stop on a hot day like yesterday. When i get home i'll generally have an electrolyte drink - not an energy drink perhaps followed by more tea! I know if i've not got things right as i'll get cramps, something i seem more prone to since my DVT 5 years ago.

The science of urine colour as an indication of hydration seems to work for me as a general guide, a lighter, straw colour and i'm fine but darker is usually associated with other indicators and for me it feels like i'm weeing razor blades! Getting some more wet inside dilutes things and maybe two hours later the wee is lighter and the discomfort passing water has passed.

My words of wisdom (even if i don't always follow them myself), keep hydrated, small sips often is better than single big hits, water is fine and can double as a cooling agent, wetting your shirt for example, not a good idea with squash! If you start feeling a bit woozy, stop and find some shade, falling off is never a good scenario! The wooziness can come on quite quickly but a warning will be a lack of energy akin to bonk.

[Psamathe]

... when it comes to eating and drinking when riding, i literally forget to do either...

I'm the same. I carry water but very rarely drink any. Cycling in the 40℃ heatwave 2018 in France and I was doing 40+ mile rides with two bottles of water in cages and never touching any 'cos I forgot. Travelling SE Asia I'd set-off on foot 1st thing exploring areas full of temples (e.g. Bagan) carrying a bottle of water and 11 miles later in the evening get back to where I was staying, bottle of water untouched and skin really salty - what I'd been seeing, etc. was so amazing I'd completely forgotten to drink.

I do tend to get a weird "warning sign" (which I seem ignore) - when I get a bit dehydrated I start to suffer PET (Patulous Eustachian Tube) where one side/tube stays open and feels weird, hear your voice inside your head and you have to put your head as upside down as possible and clear your ears to reset it and it then happens again a few minutes later. But by the time it starts to happen, drinking a load of water is not enough short term and it seems to take a few hours to return to normal. So when it happens you quickly bend over, perform the manoeuvre and forget about drinking anything. Does not happen on the bike though.

Ian

[Sweep]

If its also humid, you may find you can't sweat to lose body heat as easily as you normally do.

A wet bulb temperature of 35C is the limit to human survival:
Wet Bulb.png

yep I was reading about that somewere recently.
Question - is this "wet bulb" temperature the same as you get on some weather sites listed under the nominal temperature as "feels like", as on met office site:

https://www.metoffice.gov.uk/weather/fo ... 2022-07-11

(click on "show full forecast" at the bottom and it shows this under the nominal temp)